This is an excellent book that is very well written. The only example of bias I could add to #2 is the way in which Diamond's relationship with the people of Papua New Guinea causes him to look subjectively upon them rather than being slightly more objective. However, having said this, I don't think this detracts from his overall argument in any way. It is rather a recognition of the way that we are all marked by our own experiences and that true objectivity is impossible to attain.

The only real example of bias in this book is, I would argue, Diamond's bias in favor of geographical explanations for various historical factors.

This is, of course, not at all surprising. Diamond is writing this book to prove that geographical chance is the cause of the major differences in the development of human societies. Because of this, he picks those anecdotes about history that tend to support his point of view. When he brings up arguments that are contrary to his view, he defeats them even though there are many people who would accept those arguments.

Overall, though, this is not uncommon. Authors always discount theories that are contrary to their own. Diamond's only bias is that of most authors; he believes that he is right and treats opposing arguments accordingly.